How cancer treatment causes diet problems

Cancer treatments can affect your appetite and cause problems with eating, drinking and digestion.


The treatments most likely to cause problems with eating, drinking and digestion are:

  • chemotherapy
  • radiotherapy
  • chemoradiotherapy
  • surgery
  • targeted cancer drugs
  • immunotherapy
  • stem cell or bone marrow transplants

Sometimes treatment side effects are difficult to control. But doctors can manage most side effects, and there are things you can do to help you cope. You might have medicines to stop you feeling sick. Or have extra nutrients in high calorie and protein drinks.

In some situations, you might need drip or tube feeds.


Chemotherapy can kill healthy cells as well as cancer cells. This is what causes most of its side effects.

Different chemotherapy drugs cause different problems. The side effects that are most likely to cause problems with your eating, drinking and digestion are:

  • loss of appetite (anorexia)
  • feeling and being sick
  • diarrhoea and constipation
  • infections - with a fever you can lose your appetite, burn more calories and sweat more causing dehydration and weight loss
  • mouth problems such as changes in taste, ulcers, a sore and dry mouth, and painful swallowing


Radiotherapy damages healthy cells as well as the cancer cells. Most side effects will depend on which part of your body is treated.

Radiotherapy can cause short term diet problems. For example, radiotherapy to the head and neck can cause:

  • loss of appetite (anorexia)
  • taste changes
  • mouth ulcers
  • difficulty swallowing
  • painful swallowing
  • dry mouth
  • sore and inflamed gums
  • teeth problems

If you have treatment to your stomach or tummy (abdomen), you might have the following side effects:

  • diarrhoea
  • feeling and being sick
  • pain
  • inflammation in the bowel
  • blockages in the bowel making it difficult to absorb nutrients (long term side effect)

Radiotherapy can also cause tiredness. This can affect your appetite and put you off your food. You might not feel like cooking when you’re very tired. This can stop you from eating balanced meals and cause weight loss.


Treatment with chemotherapy and radiotherapy together is called chemoradiotherapy. 

Most people have some effects on diet during treatment. These are the same kinds of side effects you would get from radiotherapy or chemotherapy alone. But when you have both treatments together some of the side effects can be more severe. 


After any surgery, you may not feel like eating much for a while. Try to have foods and drinks high in calories and in protein. It can help with healing and fighting infection.

You are more at risk of getting an infection if you are malnourished before surgery. It also takes more time to recover from your operation.

You might need tube or drip feeding to build you up if you are very malnourished. This can be before surgery or afterwards to help you recover. You may also have a carbohydrate-rich drink before your operation.

Surgery to your digestive system often causes longer lasting problems with diet. The problems you have will depend on what you had surgery for:

  • swallowing problems after surgery to the food pipe (oesophagus) or voice box (larynx)
  • diarrhoea can be a problem after bowel, stomach or pancreatic surgery

Targeted cancer drugs

Targeted cancer drugs work by ‘targeting’ the differences in cancer cells that help them to survive and grow.

Targeted cancer drugs can cause side effects. But side effects are often fewer as these drugs affect healthy cells less compared to treatments such as chemotherapy. The side effects that are most likely to cause diet problems are:

  • feeling and being sick
  • loss of appetite (anorexia)
  • diarrhoea
  • fever
  • tiredness


Immunotherapy uses your immune system to fight cancer. It works by helping the immune system to recognise and attack cancer cells.

Some of the side effects of immunotherapy that can cause diet problems are:

  • diarrhoea
  • inflammation of the small and large bowel (enterocolitis)
  • tummy (abdominal) pain
  • sore mouth
  • fever
  • feeling and being sick

Stem cell and bone marrow transplants

You have a stem cell or bone marrow transplant for several types of cancers. You have the transplant after very high doses of chemotherapy. This treatment might also include:

  • targeted drugs with the chemotherapy
  • radiotherapy to your whole body (total body irradiation or TBI)

The radiotherapy and chemotherapy have a good chance of killing the cancer cells. But they also kill the stem cells Open a glossary item in your bone marrow.

Side effects

These treatments can cause side effects during a stem cell or bone marrow transplant. The main side effects that can cause problems with diet are:

  • feeling and being sick
  • diarrhoea
  • sore mouth and sore throat
  • taste changes
  • loss of appetite
  • feeling tired and run down
  • infection

There might also be a risk of infection form eating certain foods. It can be difficult to find a balance between what you fancy eating and what might cause an infection.

Graft versus host disease (GvHD)

Graft versus host disease (GvHD) can happen during and after a transplant using stem cells or bone marrow from a donor. The immune cells in the donor's stem or bone marrow cells attack your body cells. This can cause:

  • severe diarrhoea

  • loss of appetite

  • feeling and being sick

  • tummy (abdominal) cramps

  • difficulty swallowing

  • painful swallowing

  • weight loss

Enteral nutrition and intravenous drips

Some people with diet problems during a stem cell or bone marrow transplant can have:

  • food through a tube into their stomach (enteral nutrition)
  • intravenous (drip) feeds called parenteral nutrition (PN)
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    A Jatoi, S Kaasa and M Strijbos
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  • Cancer: Principles and Practice of Oncology (12th edition)
    VT DeVita , TS Lawrence, SA Rosenberg
    Wolters Kluwer, 2023

  • Nutrition in Cancer Patients
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    Journal of Clinical Medicine, 2019. Volume 8, 1211

  • ESPEN guidelines on nutrition in cancer patients
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    Clinical Nutrition, 2017. Volume 36. Pages 11-48

  • ESPEN practical guideline: clinical nutrition in cancer  
    M Muscaritoli and others
    Clinical Nutrition, 2021. Volume 40. Pages 2898-2913

  • The information on this page is based on literature searches and specialist checking. We used many references and there are too many to list here. If you need additional references for this information please contact with details of the particular issue you are interested in.

Last reviewed: 
13 Sep 2023
Next review due: 
14 Sep 2026

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